The use of an adjuvant as a substance which results in a specific increase in the immunogenicity of an immunogen in a vaccine formulation is now well established. As outlined by Cox and Coulter (1992), “Advances in Adjuvant Technology and Application”, in Animal Parasite Control Utilising Biotechnology, Chapter 4, Yong, W. K. CRC Press, adjuvants may possess activity in one or more of three broad categories, namely antigen presentation (the way in which individual antigen molecules are presented in a vaccine), antigen targeting (the efficacy with which the antigen payload is delivered to the appropriate effector cells of the immune system) and immune modulation (the mechanism which modifies the processing of antigens or epitopes by immune effector cells such that either the magnitude or the nature of the specific response is modified). A wide variety of adjuvants is now known. These include particulate adjuvants which are capable of forming microscopic aggregates where such aggregation is an important component of the adjuvant activity either as a result of improved presentation, improved targeting, or both. Such particulate adjuvants include aluminum salts, water-in-oil emulsions, oil-in-water emulsions, saponin (including Quil A and Iscoms), liposomes, proteosomes and microparticles (including microcapsules and microspheres). Other known adjuvants include non-particulate adjuvants which generally function by modulation of the immune response, although adjuvant presentation may be a component of their activity. These non-particulate adjuvants include peptides (such as muramyl dipeptide and its analogues), surface active molecules, nucleic acid derivatives, carbohydrate polymers, cytokines and lipid molecules. Adjuvant combinations are also well known, including Freund's complete adjuvant which combines the adjuvant activities of water-in-oil emulsions and microbacterial cells. In terms of the three discreet adjuvant functions: antigen presentation, antigen targeting, and immune modulation. the particulate adjuvants are efficient at antigen targeting, either by creating a depot to which macrophages are attracted or by being mobile and readily phagocytosed. Efficiency at antigen targeting does not effect the nature of the immune response, but will effect the economics of a vaccine by permitting a lower dose of antigen for a given effect. Immune modulation is the most complexed and least understood mode of adjuvant action. Some particulate adjuvants, particularly Iscoms, are highly immunomodulatory, however most of the others are non-immunomodulatory and require the addition of immunomodulatory molecules to enhance the immune response.